1. Field of the Invention
The instant disclosure relates to a bandgap reference voltage generating circuit; in particular, to the bandgap reference voltage generating circuit independent of system voltage and temperature.
2. Description of Related Art
With continuous inventions and improvements in high technology, consumer electronic products are gradually becoming commonly used in daily lives of people, especially various types of electronic devices such as: cell phones, digital cameras, personal digital assistants (PDA), and Tablet PCs; the consumer electronic products are popular for their features of thinness, smallness, and portability. However, when using the portable electronic devices, there is a problem of the time durance of power supply; as for now, the common solution is to mix using Ni-MH batteries or Lithium batteries with extra respectively matched chargers.
In prior art, design for bandgap reference voltage source circuit is well known in the field, these circuits are designed to provide a voltage standard independent of temperature change. The reference voltage of the bandgap reference voltage source circuit is a function of voltage Vbe developed by base-emitter voltage of the BJT and voltage difference ΔVbe developed by difference between base-emitter voltage of another two BJTs. Base-emitter voltage Vbe of the first BJT is voltage with negative temperature coefficient; which means, when temperature increases, the base-emitter voltage Vbe decreases. Voltage difference ΔVbe of another two BJTs is a voltage with positive temperature coefficient; which means, when temperature increases, the voltage difference ΔVbe increases with that. The reference voltage independent of temperature of the bandgap reference voltage source circuit may be adjusted via adjusting a sum of the voltage difference ΔVbe and the base-emitter voltage Vbe. However, General reference voltage generating circuit typically may experience a change in the ambient temperature or variation of the system voltage so as to generate the related problems of affecting the stability of the reference voltage.